Diesel particulate filters are currently being used in diesel engine exhaust systems to trap diesel particulate matter (DPM) as exhaust flows through the exhaust system from the engine, thereby preventing the trapped matter from entering the atmosphere.
While an engine is running, the existence of certain conditions enables regeneration of a DPF to be initiated. Various techniques are available for developing temperatures sufficiently high to initiate regeneration and thereafter control on-going regeneration. Regeneration is essentially a chemical process that burns off trapped DPM. For any of various reasons, not all trapped DPM may be burned off by regeneration. Moreover, the burning of trapped DPM may contribute to the build-up of ash, a non-combustible particulate.
Consequently, it may be either necessary or desirable to occasionally use a mechanical, rather than a chemical, process to remove particulate matter, such as DPM and/or ash, from a DPF. The use of compressed air has been proposed as one way to remove the particulate matter, for example as shown in the inventor's pending patent application Ser. No. 11/328,946.
Compressed air is an appropriate medium because it is readily available in service facilities and shops and it is also environmentally friendly.
One way to clean a DPF using compressed air involves certain manual operations such as removing the actual filter module that comprises a DPF substrate from a casing and manually manipulating a compressed air nozzle across a face of the substrate. Dislodged matter is ejected from an opposite face and collected in some type of collector for subsequent disposal.
Equipment that has been designed specifically for cleaning DPF's is commercially available. A DPF to be cleaned is placed in a cleaning machine with the DPF outlet, from which engine exhaust exits the DPF, coupled to a source of compressed air and with the DPF inlet, through which exhaust enters the DPF, coupled to a particulate collector. Compressed air is delivered to the outlet face of the DPF substrate in a succession of air pulses having sufficient pressure to force the air through passages in the substrate. The pulsing dislodges matter from surfaces of the substrate along the passages. The dislodged matter entrains with the flow of air through the substrate and is conveyed out of the substrate through the substrate's inlet face, leaving the DPF inlet and passing into the collector.
Such equipment may facilitate the cleaning of a DPF in certain ways, such as by reducing the amount of time and labor required to clean a DPF.
The inventor has observed that the constructions of certain DPF's and of DPF cleaning machines may prevent a DPF substrate from being substantially uniformly cleaned throughout. Uniform cleaning of a DPF substrate is important in minimizing thermal stresses in the substrate when the DPF is in use in an exhaust system. Less uniform cleaning of a substrate can result in less uniform flow of engine exhaust through the substrate and that in turn creates internal temperature differentials that stress the substrate. Such stressing may contribute to earlier aging of the DPF and therefore should be avoided or at least minimized.
When a DPF has an “open face” construction, a properly designed cleaning machine should be able to deliver compressed air pulses that provide relatively uniform cleaning throughout the substrate. Existing DPF cleaning equipment that has a frustoconical wall whose larger end is fitted to the outlet face of the substrate of an “open face” DPF and through which the pulsed air is delivered to the substrate outlet face is a design that may not provide the best uniformity in cleaning particulate matter from the substrate.
When a DPF does not have an “open face” construction, such as when the DPF casing has a frustoconical wall that enables the DPF to connect into an exhaust system, uniformity of substrate cleaning may not be readily achieved. Consequently, an improvement that promotes thorough cleaning of a DPF substrate over a greater portion of the substrate while the substrate remains in its casing would therefore be considered a desirable improvement in the state of the art.
In the same way, an improvement that promotes thorough cleaning of a DPF substrate over a greater portion of the substrate when cleaned in cleaning equipment that has a frustoconical wall through which the pulsed air is delivered to the substrate outlet face would also be considered a desirable improvement in the state of the art.